The invention relates to valves for fuel-air and metal-air batteries.
Batteries are commonly used as sources of electrical energy. A battery contains a negative electrode, “anode”, and a positive electrode, “cathode.” The anode has an active material that can be oxidized; the cathode has or consumes an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
In a metal-air electrochemical cell, oxygen is reduced at the cathode, and a metal, such as zinc, is oxidized at the anode. Oxygen is supplied to the cathode from atmospheric air external to the cell through one or more air opening(s), such as circular holes in a can that surrounds cell. In zinc-air cells, the overall electrochemical reaction within the cell results in zinc metal being oxidized to zinc ions and O2 from air being reduced to hydroxyl ions (OH−). Ultimately, zincate or zinc oxide is formed in the anode. While these chemical reactions are taking place, electrons are transferred from the anode to the cathode, providing power to the device. With certain types of zinc-air batteries a temporary cover is placed over the openings in the battery and once the battery is brought into service, the cover is removed allowing air to enter the battery and oxidize the zinc. This configuration is often used with zinc-air batteries that are used to power hearing-aids, since they are in general continuous use and are replaced often.
During use, it is desirable to provide uniform discharge of the active materials and a relatively high discharge voltage profile. It is also desirable for the cell to have a long service life.